Following the Ordinance XX that was promulgated by the government of Pakistan in 1984, which prohibited Ahmadi Muslims from any public expression of the Islamic faith, Tahir Ahmad left Pakistan and migrated to London, England, provisionally moving the headquarters of the community to the Fazl Mosque in London.[1] He is noted particularly for his question and answer sessions which he held regularly with people from around the world and for his Quranic discourses. Under his leadership, there was an acceleration in the number of Quran translations produced by the Community; and during his caliphate, the Community experienced structural and financial growth on an international level, including the launch of the first Muslim satellite television network, Muslim Television Ahmadiyya in 1994 through which he could communicate televised messages to the Community globally and have his sermons and other public engagements transmitted throughout the world through this medium.[2]

Tahir Ahmad also authored many books including, Some Distinctive Features of Islam; Christianity: A Journey from Facts to Fiction; Murder in the Name of Allah, and his magnum opus[3]Revelation, Rationality, Knowledge & Truth.

In 1993 Mirza Tahir Ahmad started an international initiation ceremony to be held every year at the annual gatherings of Ahmadis in which new converts join the community by pledging their allegiance to the Khalifa. The International Bai'at ceremony was broadcast live across the world. He often claimed that this was the historical fulfillment of the Pentecost that was destined to occur at the time of the Second Coming.[7]

Tahir Ahmad delivered annual commentaries on the Quran during the month of Ramadan. He incorporated lengthy discussions of previous commentators as well as the founder of Ahmadiyya and the Ahmadiyya Caliphs that came before him. In addition, he discussed the lexicon of the Quran and refuted many Orientalist ideas about the historicity of the Quran, Islam and the life of the Prophet Muhammad. His commentaries differed significantly from those offered by many of the classical Quranic commentators, placing emphasis on the logical and rational approach to the Quran. For example, he did not believe it was essential to rely heavily on Asbab al-nuzul (Circumstances of the Revelation) in order to understand the implications of the Quranic verses, presenting strong arguments instead that the Quran offered its own context. He delivered seven discourses on Asbab al-nuzul.[11]

Ahmad wrote a book title Revelation, Rationality, Knowledge and Truth, which was a further development on a talk he gave in Zurich, Switzerland, in 1987. It covered many topics relating to the present-day world. In this book he argued a rebuttal to the theories of biologist Richard Dawkins.[12] He also argued that Socrates was a prophet of the ancient Greeks and that several other prominent figures from history were at the level of prophethood due to their accomplishments and their influence.[13]